Chapter 3 Notes – Solving One Variable Equations
3.1 Solving One-Step Equations
Equivalent – equations that have the same solution.
Inverse Operation – Two operations that “undo” each
other.
Addition & subtraction are inverse operations.
Multiplication & division are inverse operations.
GOLDEN RULE OF EQUATIONS:
ALWAYS DO THE SAME THING TO BOTH SIDES OF THE
EQUATION!!!!!!! (equal sign splits the equation)
Properties of Equality:
Add the same number to both sides
 If a = b then a + c = b + c
Subtract the same number on both sides
 If a = b then a – c = b – c
Multiply both sides by the same number
 If a = b then ca = cb
Divide both sides by the same number
a b
then

 If a = b & c  0
c c
Flip-flop each side of the equation
 If a = b then b = a
TO SOLVE EVERY EQUATION:(with one variable)
Ask Yourself this EVERY time you solve an equation
1. Do Distributive Property.
2. Combine Like Terms.
3. Move all variables to one side.
4. Add/subtract on both sides.
5. Multiply/divide on both sides last.
*Goal-to get x by itself
Addition & Subtraction: Check Solutions
 X + -5 = -13
 X+3=7
 X + -4 = 5
 X + 6 = -15
 X – 9 = -11
 X – 4 = 22
 X – (-3) = 7
 X – (-8) = -1
 4 = -2 + x
Multiplication & Division
 4x = 12
 9x = -36
 -7x = 42
2

x  10

3
 -5x = -40
 -x = 6


1
x  30
3

x
9
2
2
x  10
3
A side Note- When Solving Equations with Decimals
Rounding rule – If not otherwise stated, round to the hundredths
place (2 numbers after the decimal).
Round off error – When you round an answer, the check will not
come out exactly.
 x + 4.84 = -131.55
2.6x = 5.9
 -3.6 + x = 5.29
-3.9x = -26.3
3.2 Two Step Equations
Work backwards, doing opposite operations in reverse order.
Examples:
2x + 4 = 8
2x + 4 = 8
-4 -4
2x = 4
2x = 4
2
2
x=2
-3x – 5 = 7
+ 5 +5
-3x = 12
-3x = 12
-3
-3
x=-4
2
x–4=2
3
+ 4 +4
1. x was multiplied by 2.
2. 4 was added.
To solve:
1. Get rid of 4 by subtracting it from both sides.
2. Get rid of 2 by dividing 2 on both sides.
1. Since 5 was subtracted, you add 5 to both sides
to undo the operation.
2. Since x was multiplied by –3, you divide both
sides by –3 to undo the operation.
1. Since 4 was subtracted, you add 4 to both sides
to undo the operation.
2
x=6
3
 3  2   3  6 
  x     
 2  3   2  1 
2. To undo multiplying by
reciprocal
2
, multiply by the
3
3
.
2
X=9
To check your solution, substitute your answer for the variable in the original equation and
work the arithmetic to see if it is equal.
1. Add/subtract on both sides.
2. Multiply/divide on both sides last.
 2x + 5 = 9

 -X + 4 = 12
8x – 9 = 23
o 10 + 3x = 37
6 – 2x = -10
1
x+2=3
4
Two-Step with Combining Like Terms on same side of equation
1. Combine Like Terms on same side of equation.
2. Add/subtract on both sides.
3. Multiply/divide on both sides last.
4x – 3x = 9
X + 5x – 5 = 1
-6x + 4x = 2
3x – 7 + x = 5
Two-Step with Distributive Property
1.
2.
3.
4.
Do Distributive Property.
Combine Like Terms on same side.
Add/subtract on both sides.
Multiply/divide on both sides last.
3(x – 2) = 18
18 – (x – 2) = 21
5x + 3(x + 4) = 28
-28 = 2(x + 3) – 5(x – 1)
Solving Equations with Decimals
Rounding rule – If not otherwise stated, round to the hundredths place (2
numbers after the decimal).
Round off error – When you round an answer, the check will not come out
exactly.
2.76x + 4.84 = -131.55
2.76x = -136.39
x = -49.41666…
x = -49.42
check:
2.76(-49.42) + 4.84 = -131.55
-136.3992 + 4.84 = -131.55
-131.5592 = -131.55
Very close but NOT exact.
3.4 Solving Equations with Variables on Both Sides
1.
2.
3.
4.
5.
Do Distributive Property.
Combine Like Terms on same side.
Move all variables to one side by adding or subtracting.
Add/subtract on both sides.
Multiply/divide on both sides last.
X + 4 = 2x – 6
7x + 19 = -2x + 55
80 – 6x = 4x
1
(12x + 16) = 10 – 3(x-2)
4
4(1 – x) + 3x = -2(x + 1)
Linear Equations & Problem Solving
Problem Solving Plan
Write a
Verbal
Model
Assign
Labels
Write an
algebraic
model
Solve
algebraic
model
Answer
the
Question
Example:
You have $60 and your sister has $135. You decide to save $5
each week, whereas your sister decides to spend $10 each week.
How long will it be before you have the as much money as your
sister?
Verbal Model:
Amount
you
have
+
Amount
you are
saving

Number
of
=
weeks
saved
Amount
your
sister
has
+
Amount
she is
spending

Labels:
Amount you have = 60
Amount you are saving = 5
Number of weeks = x
Amount your sister has = 135
Amount she is spending = 10
Algebraic Model (Equation):
60 + 5x = 135 – 10x
15x = 75
x=5
Answer to Question:
It will be 5 weeks before we have the same amount of money
Number
of weeks
spending
3.6 Solving Proportions
1.
3.
2.
4.